Ultrafast sampler with coaxial transition

ABSTRACT

An ultrafast sampler includes a series of Schottky diodes configured with a coplanar waveguide to form a nonlinear transmission line (NLTL) that compresses a local oscillator input to form a series of strobe pulses. Strobe pulses of opposite polarity are capacitively coupled to sampling diodes to obtain samples of a signal applied to a signal input. The samples are directed along an intermediate frequency waveguide to, for example, a signal processor such as an oscilloscope, for storage and analysis. The intermediate frequency waveguide is configured so that conductors of the intermediate frequency waveguide receive signal samples of a common polarity and strobe samples of opposite polarities so that portions of strobe pulses delivered to a signal processor are distinguished from signal samples. In an embodiment, the intermediate frequency waveguide and the strobe waveguide are symmetrically situated along a common axis, and conductors of the strobe waveguide are positioned between the axis and the conductors of the intermediate frequency waveguide. The sampling circuit is defined on a GaAs substrate and a coaxial-to-airline-to-substrate transition is configured to deliver signals from a coaxial cable to the sampling circuit. A signal output is configured to direct the signal back into a coaxial cable.

RELATED APPLICATIONS

This application is a division of application Ser. No. 09/833,015, filedApr. 10, 2001 now U.S. Pat. No. 7,084,716.

FIELD OF THE INVENTION

The invention pertains to methods and apparatus for high speedelectrical sampling.

BACKGROUND

The measurement of high speed electrical signals can be performed bysampling the signals at a series of time delays and then plotting signalamplitudes as a function of time. So-called “real time” digitizerstypically have sampling rates no greater than about 1-2 Gsample/sec sothat electrical signals having frequency components at frequenciesgreater than a few GHz must be characterized using so-called “equivalenttime” sampling. In equivalent time sampling, a periodic input signal issampled at a rate that is much less than the highest frequency componentof the input signal over many repetitions of the input signal and themeasurements are assembled to provide an estimate of the input signalduring a single period. Equivalent time sampling is described in, forexample, Marsland et al., U.S. Pat. No. 5,378,939 (“Marsland”) which isincorporated herein by reference.

For measurement of very high bandwidth electrical signals, equivalenttime sampling systems typically attempt to provide a short duration“strobe pulse” to one or more sampling diodes. The sampling diodes areswitched by the strobe pulse, and then a portion (i.e., a sample) of theinput signal is communicated to a signal acquisition system. Theduration and magnitude of the sample is determined by one or moretemporal properties of the strobe pulse, such as rise time, fall time,or duration. Accordingly, for high speed electrical signals, the strobepulse should have a short rise time, fall time, or duration. Examples ofsampling systems and strobe pulse generators for such sampling systemsare described in, for example, Marsland, Rodwell et al., U.S. Pat. No.5,014,108, McEwan, U.S. Pat. No. 6,060,915, Lockwood, U.S. Pat. No.4,654,600, Lockwood, U.S. Pat. No. 3,760,283, Frye, U.S. Pat. No.3,629,731, W. M. Grove, “Sampling for oscilloscopes and other RFSystems: Dc through X-band,” IEEE Trans. Microwave Theory and TechniqueMTT 14:629-635 (1966), and W. C. Whitely et al., “50 GHz sampler hybridutilizing a small shockline and an internal SRD,” IEEE MTT-S Digest(1991), which are incorporated herein by reference.

While a fast strobe pulse is needed for such a sampling system, it isalso desirable that the connection of an input signal to the samplingsystem neither introduce signal artifacts nor disturb the signal undertest. Sampling systems establish a sample window by switching a samplingdiode between conducting and non-conducting states with a fast strobepulse, and typically a portion of the strobe pulse is transmitted to thedevice under test. This portion is referred to as “strobe kickout.” Inaddition, a portion of the signal to be measured is typicallytransmitted around one or more sampling diodes and detected even withthe sampling gate closed. This signal portion is referred to as“blowby.” It will be apparent that signal artifacts caused by strobekickout and blowby are preferably avoided. Other signal artifacts arecaused by the connection of the sampling system to the signal to bemeasured. For example, the propagation of high speed electrical signalsdepends on the waveguide properties of cables and transmission lines onwhich the electrical signals propagate, and the connection of a samplingsystem to a cable or a waveguide generally loads the waveguide orpresents an unmatched impedance. As a result, electrical signalsarriving at the connection are partially reflected and these reflectionscan appear as artifacts in the measurement of the signal or can betransmitted to the signal source, thereby changing the signal presentedto the sampling system. In some prior art systems, signal artifacts areintroduced by connection of the sampling system to a device to be testedso that measurements are corrupted by the connection.

In addition to the problems listed above, the temporal resolution ofsampling systems can be limited by strobe pulse duration, strobe pulserise or fall times, or difficulties in transmitting a strobe pulse to asampling gate without degradation. Other sampling systems permitsampling only at relatively low sampling rates so that signalacquisition requires measurements over many signal periods. With suchsystems, because only a small fraction of a signal is measured, dataacquisition is slow and random noise in measurements cannot beefficiently reduced by signal averaging.

In view of these and other shortcomings, improved sampling methods,sampling apparatus, as well as methods and apparatus for connectingsignal sources to sampling systems are needed.

SUMMARY

Airline transitions are provided for delivering an electrical signalpropagating on a waveguide or cable, such as a coaxial cable to asubstrate. The transitions include one or more adapters configured toretain the cable or waveguide and deliver the electrical signal to anairline conductor that is situated along or approximately parallel to anaxis of a bore or similar cavity in a conductive housing. Inrepresentative embodiments, the conductive housing is configured toretain a substrate that is provided with an interconnect that extendsinto the cavity and electrically contacts the airline conductor. Inother representative embodiments, the cavity has a circular crosssection and the airline conductor is situated along the axis of thecavity. According to particular embodiments, the interconnect is aconductive puck that can include one or more bond balls formed by, forexample, a wire bonding process.

Sampling systems are provided that include airline transitions that areconfigured to deliver an electrical signal to a substrate that includesa sampling circuit. The sampling circuit includes a strobe waveguide, anintermediate frequency (“IF”) waveguide, and a signal input. The strobewaveguide is provided with one or more Schottky diodes, varactors, orhyperabrupt diodes configured to form a nonlinear transmission line(“NLTL”) or shockline. The NLTL is configured to produce strobe pulsesin response to a local oscillator input. The NLTL is in electricalcommunication with one or more sampling diodes that switchablycommunicates portions of a signal applied to the signal input to the IFwaveguide. The NLTL provides substantially symmetric strobe pulses butof opposite polarity to corresponding sampling diodes, and input signalportions of a common polarity are delivered to respective conductors ofthe IF waveguide as selected by application of the strobe pulses to thesampling diodes. In addition, strobe pulse portions of opposite polarityare delivered to the respective conductors of the IF waveguide. The IFwaveguide is configured to communicate the signal portions and thestrobe portions to a signal processor. Because the signal portions havea common polarity and the strobe portions have opposite polarities, thesignal processor can recover signal samples by, for example, summingsignals obtained from the IF waveguide conductors.

Sampling circuits are provided that include two sampling diodes, astrobe waveguide, and an intermediate frequency waveguide. The strobewaveguide is configured to provide a local oscillator signal (such as aseries of one or more strobe pulses) to the sampling diodes to producesignal samples that are directed to the intermediate frequencywaveguide. The waveguides are configured so that the local oscillatorsignal and the strobe signal propagate in different waveguide modes. Insome embodiments, the local oscillator signal propagates as an odd modeand the signal samples propagate as an even mode on the strobe waveguideand the intermediate frequency waveguide, respectively. According toadditional embodiments, the strobe waveguide and the intermediatefrequency waveguide are approximately symmetrically placed with respectto a common axis.

Sampling methods are provided in which sampling gates such as samplingdiodes are controlled with a strobe signal. The strobe signal ispropagated as a strobe mode along a strobe waveguide. Samples of aninput signal are directed to an intermediate frequency waveguide andpropagated in a sample mode on the intermediate frequency waveguide,wherein the strobe mode and the sample mode are different. In particularexamples, the strobe mode is an odd mode of the strobe waveguide and thesample mode is an even mode of the intermediate frequency waveguide.

These and other features and advantages of the invention are set forthbelow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a sampling circuit that is defined ona substrate and that includes a nonlinear transmission line.

FIGS. 2A-2C are schematic sectional views of the sampling circuit ofFIG. 1.

FIG. 3 is a block diagram that includes an electrical schematic diagramcorresponding to the sampling circuit of FIG. 1.

FIG. 4A is a schematic plan view of a sampling circuit that includes twononlinear transmission lines.

FIG. 4B is a partial schematic plan view of another representativeembodiment of a sampling circuit defined as a substrate.

FIGS. 5A-5D are a sectional views of a coaxial airline to substratetransition.

FIG. 6A is a plan view of a substrate portion of a housing for a coaxialairline to substrate transition.

FIGS. 6B-6C are sectional views of the substrate portion of FIG. 6A.

FIG. 6D is a plan view of a lid portion of a housing for a coaxialairline to substrate transition.

FIG. 6E is a sectional view of the lid portion of FIG. 6D.

FIG. 7 is a plan view of a substrate portion of a housing for a coaxialairline to substrate transition configured for retaining samplingcircuits such as those of FIGS. 4A-4B.

DETAILED DESCRIPTION

With reference to FIG. 1, a sampling circuit 100 is formed on asubstrate 101 and includes local oscillator (LO) inputs 102, 104 incommunication with a coplanar strip waveguide (“strobe waveguide”) 106that is defined by conductors 108, 110. A ground conductor 111 extendsaround a portion of a perimeter of the sampling circuit 100 and iselectrically connected to a ground plane defined by a conductive layeron an opposing surface (not shown in FIG. 1) of the substrate 101 withbond wires or other connection method. A conductive strap 103 connectsportions 105, 107 of a ground conductor 111. Diodes 112 _(J), J=1, . . ., 7, diodes 114 _(J), J=1, . . . , 7, and diodes 116 _(J), J=1, . . . ,7 (referred to herein collectively as diodes 112, 114, 117) electricallyconnect the conductor 108 to the conductor 110. In the example of FIG.1, the diodes 112, 114, 116 are separated longitudinally along awaveguide axis by 120 by respective distances of about 0.125 mm, 0.075mm, and 0.030 mm and have respective capacitances of 270 fF, 90 fF, and45 fF. As shown in the embodiment of FIG. 1, a total of 21 diodesinterconnect the conductors 108, 110. In additional embodiments, more orfewer diodes can be used, and the diode spacings and/or capacitances canbe varied. The sampling circuit 100 of FIG. 1 is conveniently defined ona GaAs substrate having dimensions of about 2.165 mm by 0.400 mm by 0.4mm.

Intermediate frequency (“IF”) outputs 130, 132 (also referred to hereinas sample outputs) are situated at ends of conductors 134, 136,respectively. The conductors 134, 136 are configured to form a waveguide(“intermediate frequency waveguide”) 138 and are connected to aconductive input pad 140 by respective sampling diodes 142, 144. In arepresentative example, the sampling diodes 142, 144 have capacitancesof about 8 fF. Diodes 146, 148 are provided that electrically connectthe conductors 134, 136 of the IF waveguide 138 to conductors 108, 110,respectively, of the strobe waveguide 106. The capacitances of thediodes 146, 148 are about 45 fF in the example of FIG. 1. The input pad140 is provided with a compliant input connection 141 such as a thindisc of gold, or one or more wire bond balls that can be attached by aconventional wirebonding followed by bond wire removal.

The strobe waveguide 106 and the diodes 112, 114, 116 are configured asa nonlinear transmission line (“NLTL” or “shockline”) 143 to shape alocal oscillator (“LO”) signal received at the LO inputs 102, 104 andproduce a strobe signal at the diodes 146, 148 and the sampling diodes142, 144. Because the properties of the diodes 112, 114, 116 arenonlinear functions of applied voltage, the strobe signal can have aduration, a rise time, or a fall time that is less than thecorresponding temporal characteristic of the LO signal at the LO inputs102, 104. Typically, the diodes 112, 114, 116 are arranged to produce astrobe signal having a rise time that is shorter than a rise time of theLO signal. As used herein, rise time generally refers to a time durationin which an electrical signal makes a transition from about 10% of amaximum value to about 90% of the maximum value, wherein the maximumvalue is an absolute value of applied voltage. In addition, in theembodiment of FIG. 1, diodes 112, 114, 116 are used as nonlinearelements in the NLTL 143, but other nonlinear devices can be used. Forexample, devices having capacitances that are functions of appliedvoltage such as varactors and hyperabrupt diodes can be used.

The conductors 108, 110, 111, 134, 136, the outputs 130, 132, and theinputs 102, 104 are formed by a thin conductive layer that is patterned.For example, a thin layer of gold or other metal can be used, andadditional metallic or other layers can be formed on the gold layer oron the substrate 101 prior to formation of the gold layer for variouspurposes, such as, for example, to protect the gold layer or to promotebonding to the gold layer to the substrate 101. In addition, one or morelayers can be formed between such a conductive layer and the substrate101, to, for example, promote adhesion of the gold layer to thesubstrate or to reduce migration of contaminants from the gold layerinto the substrate. Patterning of a conductive layer can be accomplishedusing photolithographic or other methods.

In the embodiment of FIG. 1, the conductors 108, 110 are situatedsymmetrically with respect to the waveguide axis 120. The conductors134, 136 of the IF waveguide are symmetrically configured with respectto, and more distant from, the waveguide axis 120.

FIGS. 2A-2C are schematic sectional views of the sampling circuit 100 ofFIG. 1. With reference to FIG. 2A, the diode 114 ₂ includes an N− dopedGaAs mesa 202 that is defined on a surface 201 of an N+ doped GaAssubstrate 200. A ground plane conductor 203 substantially covers anopposing surface 205. An ohmic contact 206 electrically connects theconductor 108 to the mesa 202 and a Schottky junction is formed betweena Schottky metal layer 208 and the mesa 202. The conductor 110 iselectrically connected to the metal layer 208 with an airbridge 210.Typically the mesa 202 and other features of the sampling circuit 100are photolithographically defined. Additional features of the diode 1142such as layers applied for passivation or to promote adhesion are notshown in FIG. 2A. Other diodes of the NLTL are similar. Ground straps211 electrically connect the conductors 105, 111 to the ground planeconductor 203.

FIG. 2B illustrates the configuration of the diodes 146, 148. The diodes146, 149 are defined by respective mesas 222, 232, Schottky metal layers223, 233, airbridges 224, 234, and ohmic contact regions 225, 235. Thesampling diodes 142, 144 are illustrated in FIG. 2C and are defined byrespective mesas 242, 252, Schottky metal layers 243, 253, airbridges244, 254, and ohmic contact regions 245, 255.

The diodes 112, 114, 116 and the strobe waveguide 106 form the NLTL 143.In other embodiments, different combinations of diodes can be used. Forexample, diodes of two or more different sizes can be arranged along thestrobe waveguide 106. In other embodiments, diode size can tapergradually along the strobe waveguide 106 so that no two diodes haveidentical design dimensions.

The strobe waveguide 106 and the IF waveguide 138 are configured to beapproximately symmetric with respect to an axis 120. In additionalembodiments, the conductors 106, 108, 134, 136 are not symmetricallyconfigured. As shown in FIG. 1, the strobe waveguide 106 and the IFwaveguide 138 are similar to coplanar stripline (“CPS”) waveguideshaving a lateral groundplane. Properties of such waveguides aredescribed in, for example, K. C. Gupta et al., Microstrip Lines andSlotlines (1996), which is incorporated herein by reference.

The operation of the sampling circuit 100 can be conveniently describedwith reference to FIG. 3 that includes a block diagram and electricalschematic diagram corresponding to a portion of the sampling circuit100. An LO signal is provided by an LO source 302 and can be, forexample, a 10 GHz sinusoidal voltage of amplitude of about 1 V, or otherelectrical signal, produced with, for example, one or more step recoverydiodes or other devices. The LO signal propagates along the NLTL 143 andis shaped by the diodes 112, 114, and 116 to produce a series ofapproximately symmetric sampling pulses 303 of duration of about 3.5 psor less. As shown in FIG. 3, the sampling pulses 303 delivered to thecapacitors 346, 348 are similar but are of opposite polarity. Thesampling pulses 303 are communicated to the sampling diodes 142, 144 viathe diodes 146, 148, shown in FIG. 3 as capacitors 346, 348,respectively. The sampling pulses 303 control the sampling diodes 142,144 so that an electrical signal (“RF signal”) from a signal source 305is communicated to the IF waveguide 138, represented in FIG. 3 as IFoutputs 307, 309. In some embodiments, a signal output 330 is alsoprovided. The portion of the electrical signal that is communicated tothe IF outputs 307, 309 (i.e., the IF waveguide 138) is referred toherein as the “sampled RF” (S_(RF)) and depends on the duration, pulseshape, and amplitude of the sampling pulses and the temporal response ofthe sampling diodes 142, 144 as well as relative timing between thesampling pulses 303 and the RF signal. Portions of the strobe pulses 303are also communicated to the IF outputs 307, 309 and are referred toherein as “strobe outputs” (S_(STROBE)). As illustrated in FIG. 3, thesampled RF communicated to each of the IF outputs 307, 309 is similarbut the strobe outputs communicated to the IF outputs 307, 309 haveopposite polarity. Thus, the signals propagating at the IF outputs 307,309 correspond to S_(RF)+S_(STROBE) and S_(RF)−S_(STROBE). Accordingly,the sampled RF can be distinguished from the strobe outputs, by, forexample, summing these signals. Typically the combined sampled RF andthe strobe outputs are delivered to a signal processor 311 such as adigitizer, oscilloscope, or other data storage and processing apparatus.While not shown in FIG. 3, the combined sampled RF and strobe outputscan be filtered, amplified, buffered, summed, or otherwise processed anddelivered as processed to the signal processor 311.

As noted above, the length of the time interval during which the RFsignal is communicated to the IF outputs 307, 309 depends on thecharacteristics of the sampling pulses 303 and the sampling diodes 142,144 as well as other factors. The sampled RF can also be controlled byadjustment of a bias applied to the sampling diodes 142, 144. Forexample, the signal processor 311 can include a bias source that appliesa bias voltage to the sampling diodes 142, 146. Alternatively, anadditional signal source can be provided to produce a bias voltage. Themagnitude and sign of the bias voltage can be selected so that thesampling diodes 142, 146 do not impede communicate of any portion of theRF signal to the IF outputs 307, 308 or so that small amplitude RFsignals are communicated efficiently to the IF outputs 307, 309. Thebias voltage can be communicated on the IF waveguide 138, and caninclude frequency components at frequencies at least as high aspermitted by the frequency response of the IF waveguide 138. Adjustmentof the bias voltage permits selection of an efficiency with which aselected portion of the RF signal is communicated to the IF outputs 307,309. For example, if the strobe pulses 303 have relative long turn-ontimes, the sampling diodes can require correspondingly long times toreach bias conditions in which the RF signal is communicated orcommunicated efficiently to the IF outputs 307, 309. Applying a biasvoltage can reduce these times. Alternatively, a bias voltage can beconfigured to prevent or reduce the communication of RF signal portionsof predetermined amplitudes to the IF outputs 307, 309.

In representative embodiments, the RF signal is a periodic signal thatrepeats at a signal repetition rate and the LO signal is arranged sothat the strobe pulses 303 are applied at a strobe repetition rate thatcan be varied to be at frequencies at or near the signal repetition rateor an integer multiple thereof. RF signal and strobe pulse relativefrequency and phase are communicated on a timing bus 321. Withsubstantially equal signal and strobe repetition rates, the RF signal isrepeatedly sampled at times at which the RF signal has a similarwaveform and an averaged sample signal value can be acquired. Adjustingthe repetition rates permits a so-called equivalent time sampledrepresentation of the RF signal to be acquired.

With reference to FIG. 4A, a sampling circuit 400 is configured for theapplication of two strobe pulses to an input pad 440. The samplingcircuit 400 includes strobe waveguides 406, 416 that comprise respectiveconductors 407, 408 and 417, 418 and respective inputs 409, 410 and 419,420. IF waveguides 426, 436 comprise respective conductors 427, 428 and437, 438 and respective inputs 429, 430 and 439, 440. Sampling diodes445 similar to the sampling diodes 142, 144 of FIG. 1 connect theconductors 427, 428, 439, 438 to the input pad 440 and diodes 447connect corresponding conductors of the strobe waveguides 405, 416 tothe IF waveguides 426, 436, respectively. A ground plane conductor 411is situated at a perimeter of a substrate 401 on which the circuit 400is defined.

Conductors 407 408 and 417, 418 of the strobe waveguides 406, 416,respectively, are interconnected with diodes 452, 453, 454 to formrespective NLTLs 402, 404. A surface of the substrate 401 opposite asurface 403 on which the sampling circuit 400 is defined is alsoprovided with a ground plane conductor that is connected to theconductor 411, but is not shown in FIG. 4.

The sampling circuit 400 can be operated in a fashion similar to that ofthe sampling circuit 100. The sampling circuit 400 is configured toprovide two strobe pulses (via the NLTLs 402, 404) and to communicatecorresponding sampled signals from the input pad 440 to corresponding IFwaveguides 426, 427. Thus, an RF signal can be sampled at a highersampling rate, or acquired by one or more signal processors.

FIG. 4B is a schematic diagram of a portion of a sampling circuit 450that includes an NLTL 492 and an IF waveguide 494. The NLTL 492 includesdiodes 495 and a strobe waveguide 496 defined by conductors 458, 460.For convenience, FIG. 4B shows illustrates all the diodes 494 of theNLTL 492 similarly although the diodes 494 generally differ in size as afunction of position along a waveguide axis 462. The IF waveguide 494includes conductors 472, 474 and diodes 464 are situated to electricallyconnect the NLTL 492 to the IF waveguide 494. Sampling diodes 466electrically connect the IF waveguide 494 to an input pad 470. As shownin FIG. 4B, the strobe waveguide 496 and the IF waveguide 494 aresituated along the waveguide axis 462, but need not be so situated. Inaddition, ground plane conductors and other features similar to those ofFIG. 1 and FIG. 4A are not shown in FIG. 4B.

The sampling circuits of FIG. 1 and FIGS. 4A-4B include one or morestrobe waveguides and one or more intermediate frequency waveguides.Placement of these waveguides symmetrically, or approximatelysymmetrically, about a common axis, facilitates distinguishing a localoscillator signal (or portions of strobe pulses produced from the localoscillator signal) and samples of a signal input. For example, thesampling circuit 100 is configured so that the local oscillator signalpropagates as an odd mode on the strobe waveguide 106 and samples of thesignal input propagate as an even mode on the intermediate frequencywaveguide 138. Portions of the local oscillator signal or strobe pulsescoupled to the intermediate frequency waveguide tend to propagate as anodd mode so that signal samples can be distinguished from the localoscillator signal by waveguide mode selection or other method. Placementof the strobe waveguide and the IF waveguide need not be completelysymmetric and a lack of symmetry generally only increases the extent towhich the local oscillator signal and the signal samples appear in acommon waveguide mode on the IF waveguide. Thus, in such arrangements,mode selection does not completely separate signal samples and the localoscillator signal.

The representative sampling circuits of FIGS. 1, 4A-4B are suitable forproviding samples of input signals obtained during time intervals ofless than a few picoseconds. However, in order to obtain samples thataccurately correspond to an input electrical signal, the inputelectrical signal must be delivered to the sampling circuit withoutintroducing signal artifacts. In addition, if the input signal to besampled is to be communicated to additional measurement apparatus or tooperational equipment for analysis or use, then delivery of the inputsignal to the sampling system should not introduce signal artifacts orotherwise degrade the signal. As used herein, sampling systems thatobtain signal samples are deliver the input signal to an output arereferred to as “feed-through samplers.” For feed-through samplers,preserving the integrity of the input signal can be a significantconsideration. In representative embodiments, an electrical signalpropagating on a coaxial cable is delivered to a coaxial airline and aconductor of the airline communicates the electrical signal to asampling circuit. The conductor also communicates the electrical signalto an output connector for delivery of the electrical signal back to acoaxial cable or other transmission line or waveguide.

With reference to FIG. 5A, an input signal propagating in a coaxialcable or other transmission line that terminates in a connector (notshown) is directed to a coax-to-airline transition (“transition”) 500that includes connector adapters 502, 504. The connector adapters areconfigured to receive or deliver electrical signals to/from cables,waveguides, or other transmission media that terminate in connectorssuch as a SMA, K, or other types of connectors. The connector adapters502, 504 are situated on a housing 506 that is generally electricallyconductive and that is electrical connected to a ground connection ofthe connector adapters. The housing 506 defines a bore 508 that issituated along an axis 509. Alternatively, the housing 506 can benonconductive but include a cavity having a conductive surface formedby, for example, thin metallic layers. A conductor 510 is situated inthe bore 508 and extends in a direction that is substantially parallelto the axis 509. In a representative example, a cross-section of thebore 508 is circular and has a radius of about 0.283 mm, the conductor510 is situated along the axis 509, and diameter of the conductor 510 isapproximately 0.241 mm. Radii of the bore 508 and the conductor 510 aretypically selected to produce a waveguide having an impedancecorresponding to an impedance of the waveguide or cable corresponding toone or both of the connector adapters 502, 504. In the representativeexample described here, the radii are selected to thatR_(bore)/R_(conductor) is approximately 2.3 to provide a waveguidehaving an impedance of about 50Ω. For other waveguide configurations, orto form a waveguide having a different impedance, differentrelationships between the dimensions of the bore 508 and the conductor510 can be used and contributions to waveguide impedance from adielectric that fills all or part of the volume defined by the bore 508can be included. The bore 508 can have various cross-sectional shapes,including, for example, rectangular, circular, and elliptical.

The conductor 510 is configured to provide communication of anelectrical transient or other electrical signal received at either ofthe connector adapters 502, 504 to an interconnect 512. The interconnect512 can be a bond wire or other flexible electrical connection that issituated to contact the conductor 510. Typically a first surface 512 a(or other portion) of the interconnect 512 presses against the conductor510 and a second surface 512 b (or other portion) connects to a bond pad516 on a substrate 518. The bond pad 516 is situated on a substrate suchas GaAs, silicon, or other material. Semiconductor substrates caninclude active electrical components or transmission lines forprocessing an electrical signal or delivering an electrical signal to adestination. In a representative embodiment, the interconnect 512 is ametallic puck formed by one or more bond balls that are attached to thebond pad 516.

In representative embodiments, the substrate 518 includes a samplingcircuit such as those of FIGS. 1 and 4A-4B, and the interconnect 512 iscorresponds to the conductive pad 140 of FIG. 1. In such embodiments,the interconnect 512 includes one or more conductive balls formed bywirebonding to the substrate 518 and removing the associated wires.

A conductive shield 520 is electrically connected to the substrate 516and to the housing 506 to reduce penetration of propagating electricfields into the substrate 516. Generally the shield 520 is electricallyconnected to ground plane conductors defined on the substrate 516. Withreference to the sampling circuit 100 of FIG. 1, the shield can beelectrically connected to the conductor 111. The shield 520 can be aflexible electrically conductive sheet material such as a thin metallicsheet, or can be a braided conductive material or a wire mesh such as agold mesh. A braided conductive material is convenient because such amaterial can be formed and wired bonded or soldered to the substrate 516and configured so that the interconnect 512 extends through an aperture571 in the shield 516 to contact the conductor 510.

The conductor 510 is supported in the housing 506 with washers 522, 524that are typically made of a low dielectric constant material thatexhibits low electrical loss in a selected frequency range. For afrequency range of from 0 Hz to about 300 GHz, a suitable material is apolytetrafluoroethlyene (TEFLON) that can be reinforced with randomlyarranged glass fibers or a glass fiber mesh. As shown in FIG. 5A, theconductor 510 extends through the washers 522, 524 to center conductorpins 526, 528 of connector adapters 502, 504, respectively. The pins526, 528 define bores 530, 532 that receive and electrically contactends of the conductor 510. Pressure of the conductor 510 against thebores 530, 532 retains the conductor 510 in the bores 530, 532. Suchpressure can be provided by, for example, forming slits in the pins 526,528 so that ends of the pins can be configured to retain the conductor510. In alternative embodiments, the conductor 510 can be attached withsolder, an electrically conductive adhesive, or in some other manner.Beads 534, 536 receive the pins 526, 528, respectively and retain thepins 526, 528 in respective connector adapters. The beads 534, 536 areconfigured to secure the pins 526, 528 so that the connection of a cableor transmission line to either or both of the pins 526, 528 does notterminate the electrical connection of the conductor 510 to theinterconnect 512. With reference to FIG. 5C, a recess 519 such as agroove is provided in the housing 506 for retention of the substrate518. As situated in the recess 519, the substrate 518 extends into thebore 508 and the shield 520 extends around the substrate 518 to thehousing 506.

The housing 506 of the transition 500 can be variously configured. Arepresentative example is shown in FIGS. 6A-6E. In this example, thehousing 506 is defined by a substrate portion 602 and a lid portion 604.The substrate portion 602 includes recesses 606, 608 configured toretain a sampling circuit or other substrate and a recess 610 thatdefines a portion of an airline bore such as the bore 508 of FIG. 5A. Arecess 612 is provided for access to the substrate retained in therecesses 606, 608. The lid portion 604 defines a recess 614 that servesas a portion of an airline bore. In addition, the substrate portion 602and the lid portion 604 are provided with one or more mounting holessuch as the holes 616 that can be tapped or otherwise configured forattachment of the lid portion 604 to the substrate portion 602. As shownin FIGS. 6A-6E, the holes are configured for use with screws, but otherfasteners or fastening methods can be used.

A substrate portion 700 of a housing configured to retain samplingcircuits such as those shown in FIGS. 4A-4B is illustrated in FIG. 7.The substrate portion 700 includes recesses 708, 710 configured toretain the sampling circuit and a recess 710 that defines a portion ofan airline bore. Recesses 712 are provided for access to the samplingcircuit and mounting holes 716 are also provided. The substrate portion700 permits access to opposing ends of a sampling circuit. As shown inFIG. 7, the substrate portion 700 is configured for a sampling circuitthat extends along an axis 720, but sampling circuits can be providedthat do not extend along a single axis, but along two or moreintersecting axes.

In additional embodiments, a transition is configured as a connectoradapter. In such embodiments, the connector adapters 502, 504 correspondto different connector types or male or female connector adapters of thesame connector type. In addition, connector adapters suitable forvarious cable types and waveguides can be provided to form acoax-to-waveguide transition. A transition provided with differentconnector adapters then can serve to adapt different connector types.

Exemplary transitions described above include an airline having a borethat is penetrated by an interconnect such as a conductive puck. Inadditional examples, the airline includes a bore that is filled orpartially filled with a dielectric, and the dielectric is provided withapertures that permit the interconnect to access an airline conductor.

The embodiments described above are examples only and it will beapparent to those skilled in the art that these embodiments can bemodified in arrangement and detail without departing from the principlesand scope of the invention. For example, shocklines or NLTLs can beconfigured to produce strobe pulses having fast rise times, fall times,or both. The invention is not to be limited by the described embodimentsand we claim all that is encompassed by the appended claims.

1. A sampling circuit, comprising; a substrate; a first sampling diodeand a second sampling diode defined on the substrate and in electricalcommunication with a signal input; a strobe waveguide, defined on thesubstrate, that includes a first conductor and a second conductorconfigured to deliver corresponding strobe pulses of opposite polarityto the first sampling diode and the second sampling diode; anintermediate frequency (IF) waveguide, defined on the substrate, andthat includes a first conductor and a second conductor that are inelectrical communication with the first sampling diode and the secondsampling diode, respectively, and configured so that signal samplesdelivered to the first and second conductors by the first sampling diodeand the second sampling diode are of the same polarity and strobeportions delivered to the first conductor and second conductor are ofopposing polarity; varactors configured with the strobe waveguide toform a nonlinear transmission line (NLTL); and respective diodes thatelectrically connect the first conductor of the IF waveguide and thesecond conductor of the IF waveguide to the first conductor of thestrobe waveguide and the second conductor of the strobe waveguide,respectively.
 2. A sampling circuit, comprising; a substrate; a firstsampling diode and a second sampling diode defined on the substrate andin electrical communication with a signal input; a strobe waveguide,defined on the substrate, that includes a first conductor and a secondconductor configured to deliver corresponding strobe pulses of oppositepolarity to the first sampling diode and the second sampling diode; andan intermediate frequency (IF) waveguide, defined on the substrate, andthat includes a first conductor and a second conductor that are inelectrical communication with the first sampling diode and the secondsampling diode, respectively, and configured so that signal samplesdelivered to the first and second conductors by the first sampling diodeand the second sampling diode are of the same polarity and strobeportions delivered to the first conductor and second conductor are ofopposing polarity, wherein the conductors of the strobe waveguide andthe conductors of the IF waveguide extend along a common axis.
 3. Thesampling circuit of claim 2, wherein the conductors of the strobewaveguide are situated symmetrically about the common axis.
 4. Thesampling circuit of claim 3, wherein the conductors of the intermediatefrequency waveguide are situated symmetrically about the common axis. 5.The sampling circuit of claim 4, wherein the conductors of the strobewaveguide are closer to the common axis than the conductors of theintermediate frequency waveguide.
 6. A sampling circuit, comprising; asubstrate; a first sampling diode and a second sampling diode defined onthe substrate and in electrical communication with a signal input; astrobe waveguide, defined on the substrate, that includes a firstconductor and a second conductor, configured to deliver correspondingstrobe pulses of opposite polarity to the first sampling diode and thesecond sampling diode; an intermediate frequency (IF) waveguide, definedon the substrate, and that includes a first conductor and a secondconductor that are in electrical communication with the first samplingdiode and the second sampling diode, respectively, and configured sothat signal samples delivered to the first and second conductors by thefirst sampling diode and the second sampling diode are of the samepolarity and strobe portions delivered to the first conductor and secondconductor are of opposing polarity; and varactors configured with thestrobe waveguide to form a nonlinear transmission line (NLTL), whereinthe strobe waveguide and the IF waveguide are coplanar waveguides thatare situated along a common axis.
 7. The sampling circuit of claim 6,wherein the IF waveguide and the strobe waveguide are situatedsymmetrically about a common axis.
 8. The sampling circuit of claim 7,wherein the substrate is GaAs.
 9. A sampling circuit, comprising: aninput configured to receive an electrical signal; a strobe waveguidesituated along an axis; an intermediate frequency waveguide situatedalong the axis; and two sampling diodes that are in electricalcommunication with the strobe waveguide and the intermediate frequencywaveguide and configured to direct samples of the electrical signal tothe intermediate frequency waveguide in response to a strobe signalpropagating on the strobe waveguide, wherein the strobe waveguide isconfigured to provide a strobe signal that propagates as an oddwaveguide mode on the strobe waveguide and the sampling diodes areconfigured to direct samples of the electrical signal to theintermediate frequency waveguide for propagation as an even mode of theintermediate frequency waveguide.
 10. The sampling circuit of claim 9wherein the strobe waveguide and the intermediate frequency waveguideare coplanar waveguides.
 11. The sampling circuit of claim 9, furthercomprising a substrate on which the strobe waveguide, the intermediatefrequency waveguide, and the sampling diodes are defined.
 12. Thesampling circuit of claim 9, further comprising a plurality of varactorsthat, in combination with the strobe waveguide, form a nonlineartransmission line.
 13. A sampling circuit that delivers signal samplesto a sample output, the sampling circuit comprising a strobe waveguideand an intermediate frequency waveguide configured so that a localoscillator signal propagates on the strobe waveguide in a waveguide modedifferent from a waveguide mode in which the signal samples propagate onthe intermediate frequency waveguide, wherein the strobe waveguide andthe intermediate frequency waveguide are approximately symmetrical withrespect to an axis.
 14. The sampling circuit of claim 13, wherein thelocal oscillator signal propagates as an odd mode on the strobewaveguide and the signal samples propagate as an even mode on theintermediate frequency waveguide.
 15. A sampling circuit, comprising: aGaAs substrate; a coplanar strip strobe waveguide and a coplanar stripintermediate frequency waveguide that are situated symmetrically about acommon axis on the GaAs substrate, wherein the strobe waveguide issituated between the intermediate frequency waveguide and the commonaxis; a plurality of varactors configured with the strobe waveguide toform a nonlinear transmission line (NLTL); capacitive couplers thatconnect corresponding conductors of the strobe waveguide and theintermediate frequency waveguide; a signal input that includes aconductive puck; and two sampling diodes situated to connect respectiveconductors of the intermediate frequency waveguide the signal input. 16.A sampling system, comprising: a sampling circuit as recited in claim15; an airline that includes a central conductor in electricalcommunication with the conductive puck and an input and output connectoradapters for connection to corresponding coaxial cables, the airlineconfigured to have an impedance corresponding to an impedance of thecoaxial cables; a local oscillator source that provides an electricalsignal to the nonlinear transmission line and, that in combination withthe NLTL, produces sampling pulses of opposite polarity; and a signalprocessor in communication with the intermediate frequency waveguidethat receives a signal sample obtained from a signal applied to theairline, wherein the signal sample received from a first conductor ofthe intermediate frequency waveguide is combined with a strobe sample ofa first polarity and the signal sample received from a second conductorof the intermediate frequency waveguide is combined with a strobe sampleof a second polarity, opposite the first polarity.